Beetroot (Beta vulgarisL.) growth and response to N supply - a case study

There is need for information on the general crop physiology and nitrogen (N) fertiliser responses of beetroot in New Zealand. We investigated the responses to N of beetroot grown in a silt loam near Hastings, Hawke's Bay. Four fertiliser treatments (0, 160, 320 or 480 kg N ha(-1)) were applied as urea, split evenly over four application times. The canopy light extinction coefficient averaged 0.64. Radiation use efficiency averaged 1.05 g MJ(-1)for the treatments that received N fertiliser. Maximum yield occurred at an N fertiliser rate around 320 kg N ha(-1). Published recommendations suggest only 225 kg N ha(-1)would have been needed. This underestimation would have led to a yield penalty of only about 6%, but decreased the risk of significant mineral being N left in the soil. We discuss approaches to account for N supply from the soil when forecasting residual mineral N and N leaching risk.